Combustor cans in a multiple can array may communicate acoustically with each other. Large pressure oscillations, also known as combustion dynamics, may result when heat release fluctuations couple with combustor can acoustic tones. Some of these combustor can acoustic tones may be in-phase with the tones of an adjacent can while other tones may be out-of-phase. The in-phase tones may excite the turbine blades in the hot gas path if the tones coincide with the natural frequency of the blades. The in-phase tones may be particularly of concern when the instabilities in different combustor cans are coherent, i.e., a strong relationship in the frequency and the amplitude of the instability in one can to the next can. Such coherent in-phase tones may excite the turbine buckets so as to lead to durability issues and thereby limit the operability of the gas turbine engine.
Current solutions to these potentially damaging in-phase coherent tones focus on combustor tuning. Such tuning may provide cans of different volume and length so as to limit the amplitude of the in-phase coherent tones near the bucket natural frequencies as compared to typical design practice limits. These tuning techniques thus may mean that the overall operability space may be limited by the in-phase coherent tones. Moreover, a significant amount of time and resources may be required to achieve frequency avoidance between the combustor and the turbine components. Further, frequency avoidance may only as accurate as the predictive capability used to achieve such.
There is thus a desire for improved systems and methods for coherence reduction between combustor components and turbine components without requiring combustor tuning and other types of conventional frequency avoidance techniques. Preferably, such systems and methods may reduce overall coherence so as to improve component lifetime without compromising system efficiency and output and without requiring extensive modifications.